Electric power steering apparatus

ABSTRACT

An electric power steering apparatus includes a steering angle control section that calculates a steering angle control current command value and the current command value using at least the steering angle control current command value. This control section has a position control section to calculate a basic steering angular velocity command value, a steering intervention compensating section to obtain a compensatory steering angular velocity command value, and a steering angular velocity control section to calculate a steering angle control current command value with the basic steering angular velocity command value, the compensatory steering angular velocity command value and an actual steering angular velocity. The steering intervention compensating section includes a compensating map section having a steering intervention compensating map that determines a characteristic of the compensatory steering angular velocity command value to a steering torque, and obtains the compensatory steering angular velocity command value by the steering torque.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2017/033114, filed Sep. 13, 2017, claiming priorities based onJapanese Patent Application Nos. 2016-181912, filed Sep. 16, 2016 and2016-215848, filed Nov. 4, 2016.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an electric power steering apparatusthat enables an automatic steering by performing an assist control and asteering angle control to a steering system by drive-controlling a motorbased on a current command value, and in particular to an electric powersteering apparatus that enables safety and reduction of uncomfortablefeeling even if a steering intervention is performed by a driver duringthe automatic steering.

Background Art

An electric power steering apparatus (EPS) which provides a steeringsystem of a vehicle with a steering assist torque (an assist torque) bymeans of a rotational torque of a motor, applies a driving force of themotor as the steering assist torque to a steering shaft or a rack shaftby means of a transmission mechanism such as gears or a belt through areduction mechanism, and performs an assist control. In order toaccurately generate the assist torque, such a conventional electricpower steering apparatus performs a feedback control of a motor current.The feedback control adjusts a voltage supplied to the motor so that adifference between a steering assist command value (a current commandvalue) and a detected motor current value becomes small, and theadjustment of the voltage supplied to the motor is generally performedby an adjustment of a duty ratio of a pulse width modulation (PWM)control.

A general configuration of the conventional electric power steeringapparatus will be described with reference to FIG. 1. As shown in FIG.1, a column shaft (a steering shaft or a handle shaft) 2 connected to asteering wheel (handle) 1 is connected to steered wheels 8L and 8Rthrough reduction gears (worm gears) 3 constituting the reductionmechanism, universal joints 4 a and 4 b, a rack-and-pinion mechanism 5,and tie rods 6 a and 6 b, further via hub units 7 a and 7 b. Inaddition, a torsion bar is inserted into the column shaft 2, for which asteering angle sensor 14 for detecting a steering angle θ of the handle1 by means of a twist angle of the torsion bar and a torque sensor 10for detecting a steering torque Tt are provided, and a motor 20 forassisting a steering force of the handle 1 is connected to the columnshaft 2 through the reduction gears 3. The electric power is supplied toa control unit (ECU) 30 for controlling the electric power steeringapparatus from a battery 13, and an ignition key signal is inputted intothe control unit 30 through an ignition key 11. The control unit 30calculates a current command value of an assist control command on thebasis of the steering torque Tt detected by the torque sensor 10 and avehicle speed V detected by a vehicle speed sensor 12, and controls acurrent supplied to the motor 20 by means of a voltage control commandvalue Vref obtained by performing a compensation or the like to thecurrent command value.

Moreover, the steering angle sensor 14 is not essential, it does notneed to be provided, and it is possible to obtain the steering anglefrom a rotational angle sensor such as a resolver connected to the motor20.

A controller area network (CAN) 40 to send/receive various informationand signals on the vehicle is connected to the control unit 30, and itis also possible to receive the vehicle speed V from the CAN 40.Further, a Non-CAN 41 is also possible to connect to the control unit30, and the Non-CAN 41 sends and receives a communication,analogue/digital signals, electric wave or the like except for the CAN40.

The control unit 30 mainly comprises a CPU (Central Processing Unit)(including an MPU (Micro Processor Unit), an MCU (Micro Controller Unit)and so on), and general functions performed by programs within the CPUare shown in FIG. 2.

The control unit 30 will be described with reference to FIG. 2. As shownin FIG. 2, the steering torque Tt detected by the torque sensor 10 andthe vehicle speed V detected by the vehicle speed sensor 12 (or from theCAN 40) are inputted into a current command value calculating section 31that calculates a current command value Iref1. The current command valuecalculating section 31 calculates the current command value Iref1 thatis a control target value of a current supplied to the motor 20 on thebasis of the inputted steering torque Tt and vehicle speed V and byusing an assist map or the like. The current command value Iref1 isinputted into a current limiting section 33 through an adding section32A. A current command value Irefm the maximum current of which islimited is inputted into a subtracting section 32B, and a deviation I(=Irefm−Im) between the current command value Irefm and a motor currentIm being fed back is calculated. The deviation I is inputted into aproportional integral (PI) control section 35 for improving acharacteristic of the steering operation. The voltage control commandvalue Vref whose characteristic is improved by the PI-control section 35is inputted into a PWM-control section 36. Furthermore, the motor 20 isPWM-driven through an inverter 37. The motor current Im of the motor 20is detected by a motor current detector 38 and is fed back to thesubtracting section 32B. The inverter 37 is comprised of a bridgecircuit of field-effect transistors (FETs) as semiconductor switchingdevices.

A rotational angle sensor 21 such as a resolver is connected to themotor 20, and a rotational angle θ is detected and outputted by therotational angle sensor 21.

Further, a compensation signal CM from a compensation signal generatingsection 34 is added to the adding section 32A, and a characteristiccompensation of the steering system is performed by the addition of thecompensation signal CM so as to improve a convergence, an inertiacharacteristic and so on. The compensation signal generating section 34adds a self-aligning torque (SAT) 34C and an inertia 34B at an addingsection 34D, further adds the result of addition performed at the addingsection 34D with a convergence 34A at an adding section 34E, and thenoutputs the result of addition performed at the adding section 34E asthe compensation signal CM.

Research and development of automatic driving technique of the vehiclehave been recently advanced, and proposals where an electric powersteering apparatus (EPS) is applied to the automatic steering includedin the technique, have been made. In the case of achieving the automaticsteering by means of the EPS, the EPS has a mechanism for an assistcontrol performed by a conventional EPS and a mechanism for a steeringangle control of controlling a steering system so that a vehicle drivesin a desired direction independently, and is generally configured so asto make outputs of these mechanisms possible to adjust. Further, in thesteering angle control, a position and velocity control having asuperior performance of responsiveness for a steering angle commandbeing a control target of a steering angle and a disturbance suppressioncharacteristic for a road surface reaction force and so on, is used. Forexample, a proportional (P) control is adopted in the position control,and a proportional integral (PI) control is adopted in the velocitycontrol.

In a case of performing the assist control and the steering anglecontrol independently and of performing the whole control by switchingthe command values being outputs from both controls, when the controlsare suddenly switched by a switch or the like, there is a possibilitythat the command values are suddenly changed, the behavior of the handlebecomes unnatural and an uncomfortable feeling to the driver may becaused. In order to take measures against this problem, an apparatusdisclosed in Japanese Unexamined Patent Publication No. 2004-17881 A(Patent Document 1), in the switching between a torque control method(corresponding to the assist control) and a rotational angle controlmethod (corresponding to the steering angle control), sets, as a finalcommand value, a value obtained by multiplying respective command valuesof both methods with coefficients (an automatic coefficient and a manualcoefficient) and by adding the multiplied results. In this way, theapparatus respectively suppresses abrupt changes of the command valuesby gradually changing the above coefficients. Further, the apparatususes a P-control in the position control of the rotational angle controlmethod, and uses a PI-control in the velocity control.

In the publication of Japanese Patent No. 3917008 B2 (Patent Document2), an automatic steering control apparatus is proposed thatautomatically performs a handle operation depending on a set steeringangle and aims at parking assist in particular. This apparatus canswitch between a torque control mode (corresponding to the assistcontrol) and a parking assist mode (corresponding to the steering anglecontrol), and performs the control by using pre-stored parking data inthe parking assist mode. Further, the apparatus performs a P-control inthe position control of the parking assist mode, and performs aPI-control in the velocity control.

The publication of Japanese Patent No. 3912279 B2 (Patent Document 3)does not directly apply the EPS, however, when an apparatus disclosed inPatent Document 3 starts a steering angle control by switching a mode toan automatic steering mode, the apparatus reduces the uncomfortablefeeling to a driver caused by an abrupt change of the handle at thestarting time by gradually increasing the steering velocity (thesteering angular velocity).

THE LIST OF PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: Japanese Unexamined Patent Publication No.    2004-17881 A-   Patent Document 2: Japanese Patent No. 3917008 B2-   Patent Document 3: Japanese Patent No. 3912279 B2

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, in Patent Document 1, since a command value (a steering anglecontrol command value) for the steering angle control is limited by thecoefficients and is outputted as the final command value while themethod is switched, the final command value decreases by the limitedamount. Due to this limitation, since the actual velocity of the motorbecomes slow compared with the command value (the steering angularvelocity command value) for the steering angular velocity calculatedbased on the steering angle control command value, a deviation occursbetween the steering angular velocity command value and the actualvelocity, an integral value of an integral (I) control in the velocitycontrol is accumulated, and a larger steering angle control commandvalue is outputted from the velocity control. As a result, since thelimitation with the coefficients is relaxed in the state where thecoefficients with which the command value (the assist control commandvalue) for the assist control is multiplied gradually increases, thesteering angle control command value becomes an excessive value as thecoefficients increases, the handle reacts to the steering angularvelocity command value excessively, and it may cause the uncomfortablefeeling such as a catching feeling and unpleasantness to the driver.

Further, the apparatus disclosed in Patent Document 1 uses the P-controlin the position control and the PI-control in the velocity control. Whenan manual input of the driver is intervened during the steering anglecontrol, since the steering angle control operates so as to follow thesteering angle control command value, it is difficult to steer by handsuntil the switching from the steering angle control to the assistcontrol is performed. Furthermore, a time delay occurs due to thedetection of the manual input and the switching operation, and theoperation for the steering intervention by the driver may not beperformed sufficiently.

The apparatus disclosed in Patent Document 2 also performs the steeringangle control by using the P-control in the position control and thePI-control in the velocity control. In the case of performing thesteering angle control in the vehicle, a disturbance and a load stateare significantly changed by the vehicle speed, friction, change of aroad surface reaction force and so on, so that the apparatus must have acontrol configuration being resistant to them. However, in the controlconfiguration of the apparatus described in Patent Document 2 alone, forexample, in the case that the road surface reaction force changes, or inthe case that a target steering angle changes rapidly, a vibrationoccurs due to a natural vibration caused by a mass damper of the handle(steering wheel) and a spring of a torsion bar, and the driver may feelit as the uncomfortable feeling or the unpleasantness.

Although the apparatus disclosed in Patent Document 3 graduallyincreases the steering angular velocity at the starting time of thesteering angle control, the integral value of the I-control accumulatesexcessively since the steering angular velocity continues increasinguntil an upper limit after beginning to increase. As a result, thesteering angle control command value becomes an excessive value, thehandle reacts to the steering angular velocity command valueexcessively, and it may cause the uncomfortable feeling to the driver.

The present invention has been developed in view of the above-describedcircumstances, and an object of the present invention is to provide anelectric power steering apparatus that achieves a manual steering evenif a steering intervention is performed by a driver during an automaticsteering, ensures more safety when a driver steers urgently, and enablesboth an assist control and a steering angle control.

Means for Solving the Problems

The present invention relates to an electric power steering apparatusthat drives a motor based on a current command value, and performs anassist control and a steering angle control for a steering system bydrive-controlling the motor, the above-described object of the presentinvention is achieved by that comprising: a steering angle controlsection that calculates a steering angle control current command valuefor the steering angle control based on at least a steering anglecommand value and an actual steering angle, wherein the steering anglecontrol section comprises: a position control section to calculate abasic steering angular velocity command value based on the steeringangle command value and the actual steering angle; a steeringintervention compensating section to obtain a compensatory steeringangular velocity command value for a steering intervention compensationdepending on a steering torque; and a steering angular velocity controlsection to calculate the steering angle control current command valuebased on a steering angular velocity command value calculated from thebasic steering angular velocity command value and the compensatorysteering angular velocity command value, and an actual steering angularvelocity; wherein the steering intervention compensating sectioncomprises a compensating map section having a steering interventioncompensating map that determines a characteristic of the compensatorysteering angular velocity command value to the steering torque, and thesteering intervention compensating section obtains the compensatorysteering angular velocity command value by the steering torque throughthe compensating map section; and wherein the electric power steeringapparatus calculates the current command value using at least thesteering angle control current command value.

The above-described object of the present invention is efficientlyachieved by that: wherein the steering intervention compensating sectionfurther includes a dead band setting section that sets values to thesteering torque within a predetermined range to zero, and thecompensatory steering angular velocity command value is obtains from thesteering torque through the dead band setting section and thecompensating map section;

or wherein the steering intervention compensating map has acharacteristic that the compensatory steering angular velocity commandvalue decreases as a vehicle speed increases;

or wherein the steering intervention compensating section furthercomprises a steering intervention phase compensating section thatperforms a phase compensation to the steering torque, and the steeringintervention compensating section obtains the compensatory steeringangular velocity command value with the steering torque through thesteering intervention phase compensating section;or wherein the steering angular velocity control section calculates thesteering angle control current command value with an integralproportional control (an I-P control) by using the steering angularvelocity command value and the actual steering angular velocity; orwherein the position control section comprises: a reference modelsection to convert the steering angle command value into a targetsteering angle using a reference model; a proportional gain section tocalculate a first basic steering angular velocity command value bymultiplying a deviation between the target steering angle and the actualsteering angle with a proportional gain; anda filter section to convert the steering angle command value into asecond basic steering angular velocity command value by using afeedforward filter (an FF filter), wherein the basic steering angularvelocity command value is calculated by adding the second basic steeringangular velocity command value to the first basic steering angularvelocity command value;or wherein a filter gain of the FF filter changes depending on a vehiclespeed;or further including an assist control section to calculate an assistcontrol current command value for the assist control based on at leastthe steering torque, wherein the current command value is calculatedfrom the assist control current command value and the steering anglecontrol current command value;or wherein for adjusting the assist control current command value, theassist control current command value is multiplied with an assistcontrol output gradual-change gain;or wherein an assist map output current obtained in the assist controlsection is multiplies with an assist map gradual-change gain;or wherein only the steering angle control is performed to the steeringsystem by multiplying the assist control current command value with theassist control output gradual-change gain whose value is zero;or wherein the steering angle control section further includes asteering angle control current command value limiting section to limitthe steering angle control current command value with a preset limitvalue.

Effects of the Invention

Since the electric power steering apparatus of the present inventionperforms the compensation of the steering intervention by using the mapin the steering angle control, it is possible to enables safety andreduction of uncomfortable feeling even if the steering intervention isoperated during the automatic steering.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a configuration diagram illustrating a general outline of anelectric power steering apparatus;

FIG. 2 is a block diagram showing a configuration example of a controlunit (ECU) of the electric power steering apparatus;

FIG. 3 is a block diagram showing a configuration example of a wholevehicle system relating to the present invention;

FIG. 4 is a block diagram showing a configuration example of aswitch-judgment and gradual-change gain generating section;

FIG. 5 is a block diagram showing a configuration example of a manualinput judging section;

FIGS. 6A, 6B and 6C are graphs showing an example of changinggradual-change gains corresponding to a steering state;

FIG. 7 is a block diagram showing a configuration example of a steeringangle control section and a switching section;

FIG. 8 is a characteristic diagram showing an example of a limit valuein a steering angle command value variable-limiting section;

FIG. 9 is a block diagram showing a configuration example of a positioncontrol section;

FIG. 10 is a characteristic diagram showing an example of changing afeedforward filter gain (an FF filter gain) of the position controlsection with respect to a vehicle speed;

FIG. 11 is a block diagram showing a configuration example (a firstembodiment) of a steering intervention compensating section;

FIG. 12 is a characteristic diagram showing an example of a steeringintervention compensating map;

FIG. 13 is a characteristic diagram showing an example of a limit valuein a velocity command value variable-limiting section;

FIG. 14 is a block diagram showing a configuration example (the firstembodiment) of a steering angular velocity control section;

FIG. 15 is a block diagram showing a configuration example of a handledamping section;

FIG. 16 is characteristic diagram showing an example of a limit value ina steering angle control current command value limiting section;

FIG. 17 is a flowchart showing an operating example of an EPS-side ECU;

FIG. 18 is a flowchart showing an operating example of theswitch-judgment and gradual-change gain generating section;

FIG. 19 is a flowchart showing a part of an operating example (the firstembodiment) of the steering angle control section;

FIG. 20 is a flowchart showing a part of the operating example (thefirst embodiment) of the steering angle control section;

FIG. 21 is a block diagram showing an example of a steering model of adriver used in simulations;

FIG. 22 is a graph showing an example of time responses of a targetangle, an actual steering angle and a steering torque in a simulationwith respect to steering intervention compensation;

FIG. 23 is a graph showing an example of changing the actual steeringangle and the steering torque in the simulation with respect to thesteering intervention compensation;

FIG. 24 is a graph showing a result of a simulation with respect tofollowability to a steering angle command value;

FIGS. 25A and 25B are characteristic diagrams showing an example of afrequency characteristic of a transfer function from a steering angularvelocity command value to an actual steering angle in a simulation withrespect to a reference model and an FF filter;

FIGS. 26A and 26B are characteristic diagrams showing an example offrequency characteristics of respective transfer functions in thesimulation with respect to the reference model and the FF filter;

FIG. 27 is a graph showing a result of the simulation with respect tothe reference model and the FF filter;

FIG. 28 is a graph showing a result of the simulation with respect tohandle vibration;

FIG. 29 is a graph showing an example of changing a target steeringangular velocity, gradual-change gains and a limit value in the case oftransferring a steering state.

FIG. 30 is a block diagram showing a configuration example (the secondembodiment) of the steering intervention compensating section;

FIG. 31 is a characteristic diagram showing a setting example of a deadband to the steering torque in the steering intervention compensatingsection;

FIG. 32 is a graph showing an example of time responses of a targetangle, an actual steering angle and a steering torque in a simulationwith respect to the dead band;

FIG. 33 is a graph showing a result of time response of the steeringtorque in a simulation with respect to the dead band;

FIG. 34 is a block diagram showing a configuration example (the thirdembodiment) of the steering angular velocity control section;

FIG. 35 is a block diagram showing a configuration example (the fourthembodiment) of the steering angular velocity control section; and

FIG. 36 is a graph showing an example (the fifth embodiment) of changinga target steering angular velocity, gradual-change gains and a limitvalue in the case of transferring a steering state.

DETAILED DESCRIPTION OF THE INVENTION

An electric power steering apparatus (EPS) according to the presentinvention performs an assist control being a function of a conventionalEPS and a steering angle control necessary to an automatic steering inan automatic driving. The assist control and the steering angle controlare performed at an assist control section and a steering angle controlsection respectively, and the EPS calculates a current command value fordrive-controlling the motor by using an assist control current commandvalue and a steering angle control current command value outputted fromrespective sections. Both of the steering angle control and the assistcontrol are performed in the automatic steering (an automatic steeringstate), and the assist control is performed in the manual steering (amanual steering state) when a driver takes part in the steering. Inorder to reduce an uncomfortable feeling caused by a steeringintervention during the automatic steering, the EPS performs a steeringintervention compensation in accordance with a steering torque.Concretely, the EPS compensates a steering angular velocity commandvalue by means of a compensation value (a compensatory steering angularvelocity command value) obtained at a steering intervention compensatingsection by using a prepared steering intervention compensating map.

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings.

First, a whole vehicle system including the electric power steeringapparatus according to the present invention will be described.

FIG. 3 shows a configuration example (the first embodiment) of the wholevehicle system relating to the present invention, which comprises an ECUequipped for a vehicle (hereinafter referred to a “vehicle-side ECU”)100, an ECU equipped for the EPS (hereinafter referred to an “EPS-sideECU”) 200, and a plant 400.

The vehicle-side ECU 100 comprises a vehicle-state quantity detectingsection 110, a switch command section 120, a target track calculatingsection 130 and a vehicle motion control section 140.

The vehicle-state quantity detecting section 110 comprises anon-vehiclecamera, a distance sensor, an angular velocity sensor, an accelerationsensor and so on, and outputs data detected by them as a vehicle-statequantity Cv to the switch command section 120, the target trackcalculating section 130 and the vehicle motion control section 140.

The switch command section 120 inputs a signal Sg for switching(shifting) an operation mode from a button, a switch or the likeprovided for a dashboard or the like with the vehicle-state quantity Cv,and outputs a switch signal SW to the EPS-side ECU 200. The operationmode has an “assist control mode” and a “steering angle control mode”,the “assist control mode” is a mode corresponding to the manualsteering, and the “steering angle control mode” is a mode correspondingto the automatic steering. The switch command section 120 determines theoperation mode considering respective data included in the vehicle-statequantity Cv based on the signal Sg which shows an intention of thedriver, and outputs the determined operation mode as the switch signalSW.

The target track calculating section 130 calculates a target track Am byusing an existing method based on the vehicle-state quantity Cv, andoutputs it to the vehicle motion control section 140.

The vehicle motion control section 140 includes a steering angle commandvalue generating section 141. The steering angle command valuegenerating section 141 generates a steering angle command value θrefbeing a control target value of the steering angle based on the targettrack Am and the vehicle-state quantity Cv, and outputs it to theEPS-side ECU 200.

The EPS-side ECU 200 comprises an EPS-state quantity detecting section210, a switch-judgment and gradual-change gain generating section 220, asteering angle control section 300, an assist control section 230, aswitching section 240, a current control and driving section 250 and amotor current detector 38.

The EPS-state quantity detecting section 210 inputs signals from anangle sensor, a torque sensor and a speed sensor, and detects anEPS-state quantity. Concretely, the angle sensor detects a handle angle(an angle at an upper side of a torsion bar) θh as an actual steeringangle θr, the torque sensor detects a steering torque Tt, and the speedsensor detects a vehicle speed V. Further, the EPS-state quantitydetecting section 210 calculates an actual steering angular velocity ωrby performing differential calculation to the actual steering angle θr.The actual steering angle θr and the actual steering angular velocity ωrare inputted into the steering angle control section 300, the steeringtorque Tt is inputted into the switch-judgment and gradual-change gaingenerating section 220, the steering angle control section 300 and theassist control section 230, and the vehicle speed V is inputted into thesteering angle control section 300 and the assist control section 230.

As well, it is possible to use a column angle (an angle at a lower sideof the torsion bar) as the actual steering angle θr, and also to use arotational angle of the motor as the actual steering angle θr byproviding a motor angle sensor (a rotational angle sensor). In addition,the actual steering angle θr and the vehicle speed V may be detected atthe vehicle-side ECU 100, and may be sent to the EPS-side ECU 200. Theactual steering angular velocity ωr may be calculated by performing adifference calculation with respect to the rotational angle detected bythe motor angle sensor and a gear ratio, or may be calculated byperforming a difference calculation with respect to the actual steeringangle θr. It is possible to insert a low pass filter (LPF) at the finalstage of the EPS-state quantity detecting section 210 to reduce a highfrequency noise, and in this case, it is possible to calculate theactual steering angular velocity ωr with a high pass filter (HPF) and again.

The switch-judgment and gradual-change gain generating section 220performs a switch judgment between the automatic steering and the manualsteering based on the switch signal SW from the vehicle-side ECU 100 andthe steering torque Tt, and determines gradual-change gains due to thejudged result. The switch-judgment and gradual-change gain generatingsection 220 obtains a steering angle control output gradual-change gainGfa1, a velocity control gradual-change gain Gfa2, a velocity commandgradual-change gain Gfa3, a steering angle command gradual-change gainGfa4, an assist control output gradual-change gain Gft1 and an assistmap gradual-change gain Gft2. The gradual-change gains Gfa1 and the Gft1are inputted into the switching section 240, the gradual-change gainsGfa2, Gfa3 and the Gfa4 are inputted into the steering angle controlsection 300, and the gradual-change gain Gft2 is inputted into theassist control section 230. The detail of the switch-judgment andgradual-change gain generating section 220 will be described later.

The steering angle control section 300 calculates a steering anglecontrol current command value IrefP1 by using the steering angle commandvalue θref from the vehicle-side ECU 100, the actual steering angle θr,the actual steering angular velocity ωr, the steering torque Tt, thevehicle speed V and the gradual-change gains Gfa2, Gfa3 and Gfa4 inorder to perform the steering angle control. The steering angle controlcurrent command value IrefP1 is inputted into the switching section 240.As well, it is possible to calculate the actual steering angularvelocity ωr not at the EPS-state quantity detecting section 210 but atsteering angle control section 300. The detail of the steering anglecontrol section 300 will be described later.

The assist control section 230 comprises, for example, the currentcommand value calculating section 31, the current limiting section 33,the compensation signal generating section 34 and the adding section 32Ain a configuration example shown in FIG. 2 in order to perform theassist control, and calculates an assist control current command valueIrefT1 equivalent to the current command value Irefm shown in FIG. 2based on the steering torque Tt and the vehicle speed V with referenceto the assist map. However, the assist control section 230 is differentfrom the configuration example shown in FIG. 2, inputs the assist mapgradual-change gain Gft2 outputted from the switch-judgment andgradual-change gain generating section 220, multiplies an output (anassist map output current) from the current command value calculatingsection 31 with the gradual-change gain Gft2, and inputs the multipliedresult into the adding section 32A. The assist map used at the currentcommand value calculating section 31 is a map that defines acharacteristic of a current command value to the steering torque Tt, isvehicle speed sensitive, and has a characteristic that the currentcommand value decreases as the vehicle speed V increases. Besides, thecurrent limiting section 33 and/or the compensation signal generatingsection 34 may be removed.

The switching section 240 calculates a current command value Iref byusing the steering angle control current command value IrefP1, theassist control current command value IrefT1 and the gradual-change gainsGfa1 and Gft1. The detail of the switching section 240 will be describedlater.

The current control and driving section 250 comprises, for example, thesubtracting section 32B, the PI-control section 35, the PWM-controlsection 36 and the inverter 37 in the configuration example shown inFIG. 2, and drive-controls the motor by using the current command valueIref and the motor current Im detected by the motor current detector 38and by the same operations as the configuration example shown in FIG. 2.

The plant 400 is a physical model of a control object that simulates acharacteristic of the driver in the steering of the handle and amechanical characteristic of an EPS and the vehicle, and comprises adriver steering transfer characteristic 410 and a mechanical transfercharacteristic 420. A mechanical system works based on a handle manualinput torque Th caused by the steering of the driver and the motorcurrent Im from the EPS-side ECU 200, and this causes a stateinformation EV with respect to the vehicle and the EPS, so that themechanical transfer characteristic 420 outputs the state information EV.The vehicle-state quantity detecting section 110 in the vehicle-side ECU100 and the EPS-state quantity detecting section 210 in the EPS-side ECU200 detect the vehicle-state quantity Cv and the EPS-state quantityrespectively from the state information EV. Since the handle manualinput torque Th caused by the steering of the driver occurs depending onthe handle angle θh included in the state information EV, the driversteering transfer characteristic 410 outputs the handle manual inputtorque Th.

Next, the switch-judgment and gradual-change gain generating section220, the steering angle control section 300 and the switching section240 in the EPS-side ECU 200 will be described in detail.

FIG. 4 shows a configuration example of the switch-judgment andgradual-change gain generating section 220, the switch-judgment andgradual-change gain generating section 220 comprises a switch judgingsection 221 and a gradual-change gain generating section 222, and theswitch judging section 221 comprises a manual input judging section 223and a steering state judging section 224.

The manual input judging section 223 judges whether a manual input isperformed or not by using the steering torque Tt. A configurationexample of the manual input judging section 223 is shown in FIG. 5. Themanual input judging section 223 comprises a smoothing filter section225, an absolute value processing section 226 and a judgment processingsection 227. The smoothing filter section 225 has a smoothing filter,smooths the steering torque Tt with the smoothing filter, and outputs asteering torque Tt′ obtained after the smoothing. The steering torqueTt′ is inputted into the absolute value processing section 226, and theabsolute value processing section 226 outputs an absolute value (anabsolute value data) |Tt′| of the steering torque Tt′. The absolutevalue |Tt′| is inputted into the judgment processing section 227. Thejudgment processing section 227 compares a predetermined threshold Tthand the absolute value |Tt′|, judges that “presence of the manual input”when the absolute value |Tt′| is larger than or equal to the thresholdTth, judges that “absence of the manual input” when the absolute value|Tt′| is smaller than the threshold Tth, and outputs the judged resultas a manual input judgment signal Jh.

The steering state judging section 224 judges a steering state with theswitch signal SW from the vehicle-side ECU 100 and the manual inputjudgment signal Jh. When the switch signal SW indicates the “assistcontrol mode” or the manual input judgment signal Jh indicates that“presence of the manual input”, the steering state judging section 224judges that the steering state is the “manual steering”. Otherwise, thatis, when the switch signal SW indicates the “steering angle controlmode” and the manual input judgment signal Jh indicates that “absence ofthe manual input”, the steering state judging section 224 judges thatthe steering state is the “automatic steering”. The judged result isoutputted as a steering state judgment signal Js.

As well, it is possible to judge the steering state with the manualinput judgment signal Jh alone. That is, the steering state judgingsection 224 may judge that the steering state is the “manual steering”when the manual input judgment signal Jh indicates that “presence of themanual input”, and may judge that the steering state is the “automaticsteering” when the manual input judgment signal Jh indicates that“absence of the manual input”.

The gradual-change gain generating section 222 determines thegradual-change gains based on the steering state judgment signal Js. Thegradual-change gains take various values depending on the steeringstate, and the gradual-change gain generating section 222 judges thesteering state with the steering state judgment signal Js.

The gradual-change gains Gfa1, Gfa2, Gfa3 and Gfa4 are 100% in theautomatic steering state, are 0% in the manual steering state, and aregradually changed in the case of shifting from the automatic steeringstate to the manual steering and in the case of shifting from the manualsteering to the automatic steering state. For example, in the case ofshifting from the automatic steering state to the manual steering, thegradual-change gains Gfa1 to Gfa4 are changed as shown in FIG. 6A. Thatis, the gradual-change gains successively decrease from a time point t1when the steering state judgment signal Js is changed from the“automatic steering” to the “manual steering”, and become 0% at a timepoint t2. On the contrary, in the case of shifting from the manualsteering to the automatic steering state, the gradual-change gainssuccessively increase from the time point when the steering statejudgment signal Js is changed to the “automatic steering”. In the casethat the steering state judgment signal Js is changed during thedecrease or the increase in the gradual-change gains (hereinafter thisstate of the decrease or the increase is referred to a “switchingstate”), the gradual-change gains turn to increase if decreasing, andturn to decrease if increasing.

As well, although the gradual-change gains are changed linearly in theswitching state in FIG. 6A, they may be changed like an S-shaped bend inorder to make the switching operation smooth. It is possible to use thegradual-change gains changed linearly through such an LPF as a primaryLPF whose cutoff frequency is 2 Hz. Further, the gradual-change gainsGfa1 to Gfa4 do not need to similarly change in conjunction, and maychange independently.

The assist control output gradual-change gain Gft1 is αt1 [%](0≤αt1≤100) in the automatic steering state, is 100% in the manualsteering state, and is gradually changed in the switching state as withthe gradual-change gains Gfa1 to Gfa4, as shown in FIG. 6B.

The assist map gradual-change gain Gft2 is αt2 [%] (0αt2≤00) in theautomatic steering state, is 100% in the manual steering state, and isgradually changed in the switching state as with the gradual-changegains Gfa1 to Gfa4, as shown in FIG. 6C.

A configuration example of the steering angle control section 300 andthe switching section 240 is shown in FIG. 7. The steering angle controlsection 300 comprises a steering angle command value variable-limitingsection 310, a variable-rate limiting section 320, a handle vibrationeliminating section 330, a position control section 340, a steeringintervention compensating section 350, a velocity command valuevariable-limiting section 360, a steering angular velocity controlsection 370, a handle damping section 380, a steering angle controlcurrent command value-limiting section 390, multiplying sections 391 and392 and adding sections 393 and 394, and the switching section 240comprises multiplying sections 241 and 242, and an adding section 243.

The steering angle command value variable-limiting section 310 in thesteering angle control section 300 limits the steering angle commandvalue θref which is received from the vehicle-side ECU 100 and is usedfor the automatic steering or the like by setting limit values (an upperlimit value and a lower limit value) in order to prevent an abnormalvalue and an excessive value caused due to a communication error or thelike from being inputted into the steering control, and outputs thelimited value as a steering angle command value θref1. The steeringangle command value variable-limiting section 310 sets the limit valuesdepending on the steering angle command gradual-change gain Gfa4 so asto set appropriate limit values in the automatic steering state and themanual steering state. For example, as shown in FIG. 8, the steeringangle command value variable-limiting section 310 judges the case wherethe steering angle command gradual-change gain Gfa4 is 100% to be theautomatic steering state, and limits the steering angle command valueθref with the limit value shown by the solid line. The steering anglecommand value variable-limiting section 310 judges the case where thesteering angle command gradual-change gain Gfa4 is 0% to be the manualsteering state, and limits the steering angle command value θref withthe limit value whose absolute value is smaller than in the automaticsteering state as shown by the broken line. The steering angle commandvalue variable-limiting section 310 judges the case where the steeringangle command gradual-change gain Gfa4 is between 0% and 100% to be theswitching state, and limits the steering angle command value θref with avalue between the solid line and the broken line. In the switchingstate, it is possible to limit the steering angle command value θrefwith the limit value of the automatic steering state shown by the solidline or the limit value of the manual steering state shown by the brokenline. Moreover, a magnitude (an absolute value) of the upper limit valueand a magnitude of the lower limit value may be different.

In order to avoid sharply changing a steering angle control currentcommand value being an output of the steering angle control due to asudden change of the steering angle command value θref, thevariable-rate limiting section 320 limits a change amount of thesteering angle command value θref1 by setting a limit value, and outputsa steering angle command value θref2. For example, a difference betweenthe previous and the present steering angle command values θref1 isdefined as the change amount. In the case that the absolute value of thechange amount is larger than a predetermined value (a limit value), thevariable-rate limiting section 320 performs an addition or a subtractionto the steering angle command value θref1 so that the absolute value ofthe change amount becomes the limit value, and outputs the result as thesteering angle command value θref2. In the case that the absolute valueof the change amount is smaller than or equal to the limit value, thevariable-rate limiting section 320 outputs the steering angle commandvalue θref1 as the steering angle command value θref2 without changingit. As with the steering angle command value variable-limiting section310, the variable-rate limiting section 320 sets the limit valuedepending on the steering angle command gradual-change gain Gfa4 so asto set an appropriate limit value in the automatic steering state andthe manual steering state. The variable-rate limiting section 320 judgesthe steering state with the steering angle command gradual-change gainGfa4. The variable-rate limiting section 320 sets the limit value to apredetermined limit value in the automatic steering state, and sets thelimit value to zero in the manual steering state so that the steeringangle command value θref2 is not changed and becomes constant.

Although the variable-rate limiting section 320 uses an intermediatevalue between both limit values in the switching state, it may use thelimit value of the automatic steering state or the limit value of themanual steering state. Moreover, it is possible to limit the changeamount by setting an upper limit value and a lower limit value insteadof setting the limit value for the absolute value of the change amount.

At the multiplying section 391, the steering angle command value θref2is multiplied with the steering angle command gradual-change gain Gfa4,and the multiplied result is outputted as a steering angle command valueθref3. This makes a target steering angle θt which is outputted from thehandle vibration eliminating section 330 as described below in theswitching state from the automatic steering state to the manual steeringstate, gradually approximate zero, and can make the steering anglecontrol act to a neutral state.

The handle vibration eliminating section 330 reduces a vibrationfrequency component included in the steering angle command value θref3.In the automatic steering, when the steering command is changed, afrequency component (the vicinity of about 10 [Hz]) exciting a vibrationcaused by springiness of the torsion bar and an inertia moment of thehandle, occurs in the steering angle command value θref3. The handlevibration eliminating section 330 reduces the handle vibration frequencycomponent included this steering angle command value θref3 by a filterprocessing using an LPF, a notch filter and so on or a phase delaycompensation, and outputs the target steering angle θt. As a filter, anyfilter may be used if it lowers a gain in a band of the handle vibrationfrequency and is possible to provide for the ECU. Providing themultiplying section 391 multiplying the steering angle commandgradual-change gain Gfa4 in front of the handle vibration eliminatingsection 330, enables a reduction of the handle vibration frequencycomponent caused by multiplying the steering angle commandgradual-change gain Gfa4. Besides, it is possible to omit the handlevibration eliminating section 330 in such a case that the handlevibration frequency component is minute.

The position control section 340 calculates the steering angularvelocity command value ωref1 for making the actual steering angle θrclose to the target steering angle θt based on the target steering angleθt and the actual steering angle θr. The position control section 340uses a reference model and a feedforward filter (an FF filter) in orderto extend a band where the actual steering angle θr is controlled withrespect to the target steering angle θt to a high frequency side. Thisenables improvement of the responsiveness (the followability) of thesteering angle control.

A configuration example of the position control section 340 is shown inFIG. 9. The position control section 340 comprises a reference modelsection 341, a proportional gain section 342, a filter section 343, asubtracting section 344 and an adding section 345.

The reference model section 341 has a transfer function G_(model)defined by the following Expression 1, and transforms the targetsteering angle θt into a target steering angle θt1 by using the transferfunction G_(model).

$\begin{matrix}{G_{model} = \frac{1}{\left( {{T_{m\; 1}s} + 1} \right)^{4}\left( {{T_{m\; 2}s} + 1} \right)^{2}}} & \left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack\end{matrix}$

-   -   where, T_(m1)=1/(2π×f_(m1)), T_(m2)=1/(2π×f_(m2)), “f_(m1)” and        “f_(m2)” are cutoff frequencies, and “s” is a Laplace operator.

The transfer function G_(model) defines a desired transfercharacteristic in a method of a model reference control. Although theorder of the denominator is “6” and the order of the numerator is “0” inthe above Expression 1, the orders are not limited to these.

The deviation θe between the target steering angle θt1 and the actualsteering angle θr is obtained at the subtracting section 344, and thedeviation θe is inputted into the proportional gain section 342. Theproportional gain section 342 multiplies the deviation θe with theproportional gain Kpp, and calculates a steering angular velocitycommand value ωrefa with the P-control.

The filter section 343 has the FF filter, and transforms the targetsteering angle θt into a steering angular velocity command value ωrefbby the FF filter. A transfer function Gf of the FF filter is defined bythe following Expression 2.

$\begin{matrix}{G_{f} = {K_{ff}\frac{G_{model}}{P_{\omega\theta}}}} & \left\lbrack {{Expression}\mspace{14mu} 2} \right\rbrack\end{matrix}$

“K_(ff)” is an FF filter gain. “P_(ωθ)” is a transfer function from thesteering angular velocity command value ωref, which is outputted fromthe adding section 393, to the actual steering angle θr, and ispredefined with identification by fitting, and so on. The FF filter gainK_(ff) is changed depending on the vehicle speed V. Since theresponsiveness of the actual steering angle to the steering anglecommand value is changed by changing a road surface reaction force and asteering intervention compensating map described below depending on thevehicle speed V, the FF filter gain K_(ff) is made vehiclespeed-sensitive. This enables the responsiveness of the actual steeringangle to the steering angle command value to be almost constant withoutdepending on the vehicle speed V. As shown in FIG. 10, for example, theFF filter gain K_(ff) is changed so as to monotonically decrease as thevehicle speed V increases from 0 km/h, to become “1.1” when the vehiclespeed V is 20 km/h, to become “1.0” when the vehicle speed V is 60 km/h,and to be kept constant at “1.0” after that.

The steering angular velocity command values ωrefa and ωrefb are addedat the adding section 345, and the added result is outputted as thesteering angular velocity command value ωref1.

As well, the processes in the reference model and the FF filter are notessential. The steering angular velocity command value ωref1 may becalculated by only the P-control in the subtracting section 344 and theproportional gain section 343.

The steering intervention compensating section 350 calculates a steeringangular velocity command value (a compensatory steering angular velocitycommand value) ωref2 for the steering intervention compensationcorresponding to the steering torque Tt. A value obtained by adding thesteering angular velocity command value ωref2 and the steering angularvelocity command value ωref1 from the position control section 340becomes a steering angular velocity command value ωref. The function ofthe steering intervention compensating section 350 enables generation ofthe steering angular velocity command value to mitigate an occurrence ofthe steering torque, and can achieve the steering intervention duringthe automatic steering. The steering intervention compensating section350 can achieve an appropriate feeling by compensating to the steeringtorque Tt by means of a steering intervention compensating map with thevehicle speed-sensitive, and phase-compensating to the steering torqueTt.

A configuration example of the steering intervention compensatingsection 350 is shown in FIG. 11. The steering intervention compensatingsection 350 comprises a steering intervention phase compensating section351 and a compensating map section 352.

The steering intervention phase compensating section 351 sets a phaselead compensation as the phase compensation, and converts the steeringtorque Tt into the steering torque Tt1. The steering intervention phasecompensating section 351 performs the phase lead compensation, forexample, with a primary filter where a cutoff frequency of a numeratoris 1.0 [Hz] and a cutoff frequency of a denominator is 1.3 [Hz]. Thisenables improvement of feeling without resistance and catching feelingin such a case of suddenly steering. Moreover, the steering interventionphase compensating section 351 may be omitted in such a case of focusingon a cost.

The compensating map section 352 has the steering interventioncompensating map and calculates the steering angular velocity commandvalue ωref2 by using the steering intervention compensating map. Thesteering intervention compensating map is a map by which thecharacteristic of the steering angular velocity command value to thesteering torque is determined, changes its value depending on thevehicle speed, and calculates the steering angular velocity commandvalue ωref2 by using the steering torque Tt1 and the vehicle speed V.The steering intervention compensating map is adjusted by tuning. Forexample, as shown in FIG. 12, the steering angular velocity commandvalue increases as the steering torque increases, and decreases as thevehicle speed increases. This enables heavy feeling at a higher vehiclespeed. The assist map used at the assist control section 230 also has acharacteristic that that the assist control current command valuedecreases as the vehicle speed increases. In the case that the steeringintervention is performed by the driver at a high speed running,increases in the steering angular velocity command value and the assistcontrol current command value are suppressed, the steering does notbecome sudden, and the safe steering is enabled.

As well, the steering intervention phase compensating section 351 may bedisposed at the subsequent stage of the compensating map section 352.

The steering angular velocity command value ωref1 outputted from theposition control section 340 and the steering angular velocity commandvalue ωref2 outputted from the steering intervention compensatingsection 350 are added at the adding section 393, and the added result isoutputted as the steering angular velocity command value ωref.

The steering angular velocity command value ωref is multiplied with thevelocity command gradual-change gain Gfa3 at the multiplying section392, and the multiplied result is outputted as a steering angularvelocity command value ωrefg. The velocity command gradual-change gainGfa3 is used in order to achieve smooth switching in the case ofshifting from the manual steering state to the automatic steering state.Moreover, the velocity command gradual-change gain Gfa3 is changed insynchronization with the steering angle control output gradual-changegain Gfa1 by which the steering angle control current command valueIrefP1 is multiplied (the synchronization may not be perfect).

The velocity command value variable-limiting section 360 limits thesteering angular velocity command value ωrefg by setting limit values(an upper limit value and a lower limit value), and outputs a targetsteering angular velocity ωt. The limit values are set depending on thevelocity command gradual-change gain Gfa3. For example, when thevelocity command gradual-change gain Gfa3 is smaller than apredetermined threshold, magnitudes (absolute values) of the limitvalues are small values as shown by the broken line in FIG. 12, and whenit is larger than or equal to the predetermined threshold, themagnitudes of the limit values are increased to the values shown by thesolid line.

As well, it is possible that the predetermined threshold is set to anyvalue of the velocity command gradual-change gain Gfa3 in the switchingstate, the magnitudes of the limit values are fixed at the small valuesshown by the broken line when the gradual-change gain Gfa3 is smallerthan the predetermined threshold, and the magnitudes of the limit valuesare gradually increased to the values shown by the solid line. Further,the magnitude of the upper limit value and the magnitude of the lowerlimit value may be different.

The steering angular velocity control section 370 inputs the targetsteering angular velocity ωt, the actual steering angular velocity ωrand the velocity control gradual-change gain Gfa2, and calculates asteering angle control current command value IrefW by using aproportional preceding type PI (I-P) control so that the actual steeringangular velocity ωr follows the target steering angular velocity ωt.

A configuration example of the steering angular velocity control section370 is shown in FIG. 14. The steering angular velocity control section370 comprises gain multiplying sections 371 and 372, an integratingsection 373, subtracting sections 374 and 375, and a multiplying section376.

The gain multiplying section 371 multiplies a deviation ωe (=ωt−ωr)between the target steering angular velocity ωt and the actual steeringangular velocity ωr, which is calculated at the subtracting section 374,with a gain Kvi, and outputs an operation amount D1. The integratingsection 373 integrates the operation amount D1, and calculates a controlamount Ir1. At the multiplying section 376, the control amount Ir1 ismultiplied with the velocity control gradual-change gain Gfa2, and themultiplied result is outputted as a control amount Ir3. Themultiplication of the velocity control gradual-change gain Gfa2 isperformed in order to achieve the smooth switching between the manualsteering state and the automatic steering state, and this can relax aninfluence of accumulating an integral value in the steering angularvelocity control at the time of the switching. The gain multiplyingsection 372 multiplies the actual steering angular velocity ωr with again Kvp, and outputs a control amount Ir2. At the subtracting section375, a deviation (=Ir3−Ir2) between the control amounts Ir3 and Ir2 iscalculated, and the subtracted result is outputted as the steering anglecontrol current command value IrefW.

As well, as the integral of the integrating section 373, any method canbe used if it is an integral method possible to achieve in theimplementation, and the integrating section 373 can be constituted of aprimary delay transfer function and a gain in the case of usingpseudo-integral. Further, the velocity control gradual-change gain Gfa2may be changed in synchronization with the steering angle control outputgradual-change gain Gfa1.

Moreover, although the steering angular velocity control section 370uses the I-P control, a control method generally used may be used if itcan make the actual steering angular velocity follow the target steeringangular velocity. For example, it is possible to use a PI-control, atwo-degree of freedom PI-control, a model reference control, a modelmatching control, a robust control, a control method that estimates adisturbance and combines a compensating means for counteracting adisturbance component with a part of it, and so on.

The handle damping section 380 damps a handle vibration based on thesteering torque Tt being a torsion bar torque signal. Although thehandle vibration eliminating section 330 also has an effect on thehandle vibration in the automatic steering, the handle damping section380 can further improve the effect. The handle damping section 380 dampsthe handle vibration with a gain and a phase compensation, and outputs asteering angle control current command value IrefV operating toeliminate a twist of the torsion bar. Further, the handle dampingsection 380 operates to reduce a twist angle, and has also an effect ofreducing catching uncomfortable feeling occurring when the manual inputof the driver is intervened.

A configuration example of the handle damping section 380 is shown inFIG. 15. The handle damping section 380 comprises a gain section 381 anda damping phase compensating section 382. The gain section 381multiplies the steering torque Tt with a gain Kv, and outputs a controlamount Irv. The damping phase compensating section 382 is constitutedof, for example, a primary filter, and converts the control amount Irvinto the steering angle control current command value IrefV. The dampingphase compensating section 382 may be constituted of a phasecompensation filter whose order is larger than or equal to two insteadof the primary filter.

At the adding section 394, the steering angle control current commandvalue IrefW outputted from the steering angular velocity control section370 and the steering angle control current command value IrefV outputtedfrom the handle damping section 380, are added, and the added result isoutputted as a steering angle control current command value IrefP2.

The steering angle control current command value limiting section 390limits the steering angle control current command value IrefP2 bysetting limit values (an upper limit value and a lower limit value) inorder to prevent an excessive output, and outputs the steering anglecontrol current command value IrefP1. For example, the steering anglecontrol current command value limiting section 390 limits the steeringangle control current command value IrefP2 by setting the upper limitvalue and the lower limit value as shown in FIG. 16. Besides, amagnitude (an absolute value) of the upper limit value and a magnitudeof the lower limit value may be different.

The switching section 240 comprises the multiplying sections 241 and242, and the adding section 243.

At the multiplying section 241 of the switching section 240, thesteering angle control current command value IrefP1 outputted from thesteering angle control section 300 is multiplied with the steering anglecontrol output gradual-change gain Gfa1 outputted from theswitch-judgment and gradual-change gain generating section 220, and themultiplied result is outputted as a steering angle control currentcommand value IrefP. The steering angle control output gradual-changegain Gfa1 is used in order to smoothly perform the switching operationbetween the manual steering state and the automatic steering state andto achieve the uncomfortable feeling to the driver, the safety and soon. At the multiplying section 242, the assist control current commandvalue IrefT1 outputted from the assist control section 230 is multipliedwith the assist control output gradual-change gain Gft1, and themultiplied result is outputted as an assist control current commandvalue IrefT. The assist control output gradual-change gain Gft1 is usedin order to smoothly perform the switching operation between the manualsteering state and the automatic steering state and to achieve thesteering intervention by the driver in the automatic steering. At theadding section 243, the steering angle control current command valueIrefP and the assist control current command value IrefT are added, andthe added result is outputted as the current command value Iref.

The assist map gradual-change gain Gft2 used in the above assist controlsection 230 is also used for the same purpose as the assist controloutput gradual-change gain Gft1. In the automatic steering state,setting the gradual-change gain Gft1 to the value αt1 and thegradual-change gain Gft2 to the value αt2 as shown in FIGS. 6B and 6Cand adjusting the value αt1 and the value αt2, enable improvement of thesafety of the system and the suppression of occurrence of the vibration.Further, if it is possible to maintain the safety of the system in theautomatic steering state, it is possible to set the value αt1 0% on andthe value αt2 to 100% simply. In this case, since the value αt1 is 0%,the assist control current command value IrefT becomes a zero command,and this means to achieve the steering intervention even without theassist control.

In such a configuration, an operating example of the EPS-side ECU 200will be described with reference to flowcharts shown in FIGS. 17 to 20.

When the operation is started, the EPS-state quantity detecting section210 detects the actual steering angle θr, the steering torque Tt and thevehicle speed V (Step S10), outputs the actual steering angle θr to thesteering angle control section 300, outputs the steering torque Tt tothe switch-judgment and gradual-change gain generating section 220, thesteering angle control section 300 and the assist control section 230,and outputs the vehicle speed V to the steering angle control section300 and the assist control section 230. Furthermore, the EPS-statequantity detecting section 210 calculates the actual steering angularvelocity ωr with the actual steering angle θr (Step S20), and outputsthe actual steering angular velocity ωr to the steering angle controlsection 300.

The switch-judgment and gradual-change gain generating section 220inputting the steering torque Tt judges the switching between theautomatic steering and the manual steering based on the presence/absenceof the input of the switch signal SW outputted from the vehicle-side ECU100, determines the gradual-change gains on the basis of the judgedresult (Step S30), outputs the gradual-change gains Gfa2, Gfa3 and Gfa4to the steering angle control section 300, outputs the gradual-changegain Gft2 to the assist control section 230, and outputs thegradual-change gains Gfa1 and the Gft1 to the switching section 240. Adetailed operation of the switch-judgment and gradual-change gaingenerating section 220 will be described below.

The steering angle control section 300 inputs the steering angle commandvalue θref outputted from the vehicle-side ECU 100, the actual steeringangle θr, the actual steering angular velocity ωr, the steering torqueTt and the vehicle speed V which are outputted from the EPS-statequantity detecting section 210, and the gradual-change gains Gfa2, Gfa3and Gfa4 outputted from the switch-judgment and gradual-change gaingenerating section 220, calculates the steering angle control currentcommand value IrefP1 by using them (Step S40), and outputs the steeringangle control current command value IrefP1 to the switching section 240.A detailed operation of the steering angle control section 300 will bedescribed below.

The assist control section 230 inputs the steering torque Tt, thevehicle speed V and the assist map gradual-change gain Gft2, andcalculates the assist map output current (current value) by the sameoperation as the current command value calculating section 31 shown inFIG. 2 (Step S50). The assist control section 230 multiplies the assistmap output current with the assist map gradual-change gain Gft2 (StepS60), performs the same operations as the adding section 32A, thecurrent limiting section 33 and the compensation signal generatingsection 34 which are shown in FIG. 2 for the multiplied result,calculates the assist control current command value IrefT1 (Step S70),and outputs the assist control current command value IrefT1 to theswitching section 240.

The switching section 240 multiplies the inputted steering angle controlcurrent command value IrefP1 with the steering angle control outputgradual-change gain Gfa1 at the multiplying section 241 (Step S80), andoutputs the steering angle control current command value IrefP being themultiplied result to the adding section 243. Further, the switchingsection 240 multiplies the inputted assist control current command valueIrefT1 with the assist control output gradual-change gain Gft1 at themultiplying section 242 (Step S90), and outputs the assist controlcurrent command value IrefT being the multiplied result to the addingsection 243. The adding section 243 adds the steering angle controlcurrent command value IrefP and the assist control current command valueIrefT (Step S100), and outputs the current command value Iref being theadded result to the current control and driving section 250.

By using the current command value Iref and the motor current Imdetected by the motor current detector 38, the current control anddriving section 250 performs the control so that the motor current Imfollows the current command value Iref by the same operations as thesubtracting section 32B, the PI-control section 35, the PWM-controlsection 36 and the inverter 37 which are shown in FIG. 2 (Step S110),and drive-controls the motor.

The detail of the operating example of the switch-judgment andgradual-change gain generating section 220 will be described withreference to a flowchart shown in FIG. 18. Moreover, the “manualsteering” is set on the steering state judgment signal Js as an initialvalue in the steering state judging section 224.

The inputted steering torque Tt is inputted into the manual inputjudging section 223 in the switch judging section 221. The manual inputjudging section 223 smooths the steering torque Tt at the smoothingfilter section 225 (Step S210), and obtains the absolute value |Tt′| ofthe steering torque Tt′ obtained by the smoothing at the absolute valueprocessing section 226 (Step S220). The absolute value |Tt′| is inputtedinto the judgment processing section 227. When the absolute value |Tt′|is larger than or equal to the threshold Tth (Step S230), the judgmentprocessing section 227 judges that “presence of the manual input” (StepS240). When the absolute value |Tt′| is smaller than the threshold Tth(Step S230), the judgment processing section 227 judges that “absence ofthe manual input” (Step S250). The judgment processing section 227outputs the manual input judgment signal Jh being the judged result tothe steering state judging section 224.

The steering state judging section 224 inputs the switch signal SW andconfirms whether the switch signal SW is inputted or not (Step S260). Inthe case of inputting the switch signal SW, the steering state judgingsection 224 updates the steering state judgment signal Js to the “manualsteering” (Step S280) when the switch signal SW indicates the “assistcontrol mode” or the manual input judgment signal Jh indicates that“presence of the manual input” (Step S270), otherwise (Step S270), thesteering state judging section 224 updates the steering state judgmentsignal Js to the “automatic steering” (Step S290). In the case of notinputting the switch signal SW, the steering state judgment signal Js isleft as it is. The steering state judgment signal Js is inputted intothe gradual-change gain generating section 222.

The gradual-change gain generating section 222 confirms the value of thesteering state judgment signal Js (Step S300). When the steering statejudgment signal Js is the “manual steering”, the gradual-change gaingenerating section 222 changes the respective gradual-change gains (Gfa1to Gfa4, Gft1 and Gft2) to the values in the manual steering state (0%for Gfa1 to Gfa4, and 100% for Gft1 and Gft2) (Step S310). When thesteering state judgment signal Js is the “automatic steering”, thegradual-change gain generating section 222 changes the respectivegradual-change gains to the values in the automatic steering state (100%for the gradual-change gains Gfa1 to Gfa4, the value αt1 for thegradual-change gain Gft1, and the value αt2 for the gradual-change gainGft2) (Step S320).

The detail of the operating example of the steering angle controlsection 300 will be described with reference to flowcharts shown inFIGS. 19 and 20.

The steering angle command value variable-limiting section 310 confirmsthe value of the inputted steering angle command gradual-change gainGfa4 (Step S410). The steering angle command value variable-limitingsection 310 sets the limit values to the limit values “in the manualsteering” shown in FIG. 8 (Step S420) when the Gfa4 is 0%, sets thelimit values to the limit values “in the automatic steering” shown inFIG. 8 (Step S430) when the gradual-change gain Gfa4 is 100%, and setsthe limit values to intermediate values (Step S440) when thegradual-change gain Gfa4 is between 0% and 100%. The steering anglecommand value variable-limiting section 310 limits the steering anglecommand value θref inputted from the vehicle-side ECU 100 by using theset limit values (Step S450), and outputs the steering angle commandvalue θref1.

The steering angle command value θref1 is inputted into thevariable-rate limiting section 320 with the steering angle commandgradual-change gain Gfa4 and the actual steering angle Gr. Thevariable-rate limiting section 320 confirms the value of the steeringangle command gradual-change gain Gfa4 (Step S460). When thegradual-change gain Gfa4 is 0%, the variable-rate limiting section 320sets the limit value to zero (Step S470), and sets the value of thestored previous steering angle command value θref1 to the value of theactual steering angle θr (Step S471). The Step S471 is a step forsuppressing a sudden change of the steering angle command value bystarting in a state of matching the steering angle command value θref1with the actual steering angle θr since a value at the time ofterminating the previous steering control remains at the time ofstarting the steering control where the gradual-change gain Gfa4 becomeslarger than 0% and a handle may suddenly move by the sudden change ifusing its value as it is. The variable-rate limiting section 320 setsthe limit value to the predetermined value (Step S480) when thegradual-change gain Gfa4 is 100%, and sets the limit value to theintermediate value (Step S490) when the gradual-change gain Gfa4 isbetween 0% and 100%. The variable-rate limiting section 320 calculatesthe difference (the change amount) between the steering angle commandvalue θref1 and the previous steering angle command value θref1 (StepS500). When the absolute value of the change amount is larger than thelimit value (Step S510), the variable-rate limiting section 320increases or decreases the steering angle command value θref1 so thatthe absolute value of the change amount becomes the limit value (StepS520), and outputs the result as the steering angle command value θref2(Step S530). When the absolute value of the change amount is smallerthan or equal to the limit value (Step S510), the variable-rate limitingsection 320 outputs the steering angle command value θref1 as thesteering angle command value θref2 (Step S530).

The steering angle command value θref2 is multiplied with the steeringangle command gradual-change gain Gfa4 at the multiplying section 391(Step S540), and the multiplied result is outputted as the steeringangle command value θref3. The steering angle command value θref3 isinputted into the handle vibration eliminating section 330.

The handle vibration eliminating section 330 reduces the steering anglecommand value θref3 due to the vibration frequency component (StepS550), and outputs the reduced result as the target steering angle θt tothe position control section 340.

The target steering angle θt is inputted into the reference modelsection 341 and the filter section 343 in the position control section340. The reference model section 341 transforms the target steeringangle θt into the target steering angle θt1 by using the aboveExpression 1 (Step S560). The target steering angle θt1 isaddition-inputted into the subtracting section 344, the actual steeringangle θr is subtraction-inputted into the subtracting section 344, andthe deviation θe between the target steering angle θt1 and the actualsteering angle θr is obtained (Step S570). The deviation θe is inputtedinto the proportional gain section 342. The proportional gain section342 multiplies the deviation θe with the proportional gain Kpp, andcalculates the steering angular velocity command value ωrefa (StepS580). The filter section 343 inputting the target steering angle θtinputs also the vehicle speed V, obtains the FF filter gain K_(ff) fromthe vehicle speed V by using the characteristic shown in FIG. 10, andtransforms the target steering angle θt into the steering angularvelocity command value ωrefb by using the above Expression 2 (StepS590). The steering angular velocity command values ωrefa and ωrefb areadded at the adding section 345 (Step S600), the steering angularvelocity command value ωref1 is outputted, and the steering angularvelocity command value ωref1 is inputted into the adding section 393.

Meanwhile, the steering intervention compensating section 350 inputs thevehicle speed V and the steering torque Tt, the vehicle speed V isinputted into the compensating map section 352 and the steering torqueTt is inputted into the steering intervention phase compensating section351. The steering intervention phase compensating section 351 convertsthe steering torque Tt into the steering torque Tt1 by the phasecompensation (Step S610). The steering torque Tt1 and the vehicle speedV are inputted into the compensating map section 352. The compensatingmap section 352 calculates the steering angular velocity command valueωref2 to the steering torque Tt1 by using a steering interventioncompensating map determined from the vehicle speed V based on thecharacteristic shown in FIG. 12 (Step S620). The steering angularvelocity command value ωref2 is inputted into the adding section 393.

The steering angular velocity command values ωref1 and ωref2 inputtedinto the adding section 393 are added (Step S630), and the added resultis outputted as the steering angular velocity command value ωref. Thesteering angular velocity command value ωref is multiplied with thevelocity command gradual-change gain Gfa3 at the multiplying section 392(Step S640), and the multiplied result is inputted as the steeringangular velocity command value ωrefg into the velocity command valuevariable-limiting section 360.

The velocity command value variable-limiting section 360 inputs thevelocity command gradual-change gain Gfa3 with the steering angularvelocity command values ωrefg, and confirms the value of the velocitycommand gradual-change gain Gfa3 (Step S650). The velocity command valuevariable-limiting section 360 sets the limit values to the limit valuesshown by “Gfa3 SMALL” in FIG. 13 (Step S660) when the gradual-changegain Gfa3 is smaller than the predetermined threshold, and sets thelimit values to the limit values shown by “Gfa3 LARGE” (Step S670) whenthe gradual-change gain Gfa3 is larger than or equal to thepredetermined threshold. The velocity command value variable-limitingsection 360 limits the steering angular velocity command values ωrefg byusing the set limit values (Step S680), and outputs the target steeringangular velocity cot. The target steering angular velocity cot isinputted into the steering angular velocity control section 370.

The steering angular velocity control section 370 inputs the actualsteering angular velocity ωr and the velocity control gradual-changegain Gfa2 with the target steering angular velocity cot. The targetsteering angular velocity cot is addition-inputted into the subtractingsection 374, the actual steering angular velocity ωr issubtraction-inputted into the subtracting section 374, and the deviationωe between the target steering angular velocity ωt and the actualsteering angular velocity ωr is inputted into the gain multiplyingsection 371 (Step S690). The gain multiplying section 371 multiplies thedeviation ωe with the gain Kvi (Step S700), and outputs the operationamount D1. The operation amount D1 is inputted into the integratingsection 373. The integrating section 373 calculates the control amountIr1 by integrating the operation amount D1 (Step S710), and outputs thecontrol amount Ir1 to the multiplying section 376. The multiplyingsection 376 multiplies the control amount Ir1 with the velocity controlgradual-change gain Gfa2 (Step S720), and outputs the control amountIr3. The control amount Ir3 is addition-inputted into the subtractingsection 375. The actual steering angular velocity ωr is inputted alsointo the gain multiplying section 372. The gain multiplying section 372multiplies the actual steering angular velocity ωr with the gain Kvp(Step S730), and outputs the control amount Ir2. The control amount Ir2is subtraction-inputted into the subtracting section 375. At thesubtracting section 375, the deviation between the control amounts Ir3and Ir2 is calculated (Step S740), and is outputted as the steeringangle control current command value IrefW to the adding section 394.

The steering torque Tt is inputted also into the handle damping section380. In the handle damping section 380, the gain section 381 multipliesthe inputted steering torque Tt with the gain Kv (Step S750), andoutputs the control amount Irv. The control amount Irv isphase-compensated at the damping phase compensating section 382 (StepS760), and the phase-compensated result is outputted as the steeringangle control current command value IrefV. The steering angle controlcurrent command value IrefV is outputted to the adding section 394.

The steering angle control current command values IrefW and IrefVinputted into the adding section 394 are added (Step S770), and theadded result is inputted as the steering angle control current commandvalue IrefP2 into the steering angle control current commandvalue-limiting section 390.

The steering angle control current command value-limiting section 390limits the steering angle control current command value IrefP2 by usingthe limit values of the characteristic shown in FIG. 16, and outputs thesteering angle control current command value IrefP1 (Step S780).

As well, the order of the operation of the steering angle controlsection 300 and the operation of the assist control section 230 may bereversed, or the operations may be performed in parallel. In theoperation of the steering angle control section 300, the order of theoperation to the calculation of the steering angular velocity commandvalue ωref1 and the operation to the calculation of the steering angularvelocity command value ωref2, which are inputted into the adding section393, the order of the operation to the calculation of the steering anglecontrol current command value IrefW and the operation to the calculationof the steering angle control current command value IrefV, which areinputted into the adding section 394, and so on, may be reversedrespectively, or both operations may be performed in parallelrespectively.

Effects of the present embodiment will be described based on results ofsimulations.

In the simulations, a vehicle motion model and a steering model of thedriver are set as a plant model of the plant 400. It is possible to usea model shown in, for example, “Motion and control of an automobile”,Masato Abe, Tokyo Denki University, Tokyo Denki University Press,published on Sep. 20, 2009, second impression of the first edition,chapter 3 (p. 49-105), chapter 4 (p. 107-130) and chapter 5 (p.131-147), as the vehicle motion model, and use a model shown in, forexample, “A study with respect to an estimation of steering feeling of avehicle considering a musculoskeletal characteristic of an arm”, DaisukeYokoi, master's thesis, Master's Programs, Mechanical Engineering,Graduate School of Engineering, Mie University, received on Feb. 6,2007, chapter 2 (p. 3-5) and chapter 3 (p. 6-9) (Reference Document) asthe steering model. It is possible to use another model without limitedto these. The steering model used in the present simulation is shown inFIG. 21 as a reference. In FIG. 21, “C_(arm)” and “C_(palm)” areviscosity coefficients, “K_(arm)” and “K_(palm)” are spring constants,and “I_(arm)” is an inertia moment of an arm. The handle angle θh isinputted from a mechanical model (a mechanical transfer characteristic)to the steering model (a driver-steering transfer characteristic), andthe handle manual input torque Th is outputted from the steering modelto the mechanical model. Hereinafter, a target angle described inReference Document is referred to a driver's target angle (a steeringtarget angle) θarm. Further, the model shown in Reference Document addsa mass system of an arm to a column inertia moment, however, by defininga force applied from a palm to the handle as the handle manual inputtorque Th, no hindrance occurs even if performing a simulation assumingthat the spring constant K_(palm) and the viscosity coefficient C_(palm)which operate between an angle of a palm and the handle angle θh arelarge enough, and the present simulation is performed in this way. It isalso assumed that followability of the motor current to a currentcommand value is fast enough, an influence by operation of the currentcontrol and driving section 250 is slight, and the current command valueis equal to the motor current. Furthermore, the vehicle speed is assumedconstant.

First, an effect of the steering intervention compensation will bedescribed.

Assuming the steering angle command value θref to be constant at 0[deg], a simulation of the automatic steering where the driver's targetangle θarm is inputted is performed. As a reference, time responses ofthe actual steering angle θr and the steering torque Tt to a time changeof the driver's target angle θarm in a simulation considering thesteering model of the driver under the same conditions, are shown inFIG. 22. In FIG. 22, the vertical axis indicates an angle [deg] and asteering torque [Nm], the horizontal axis indicates a time [sec], thethick solid line shows the driver's target angle θarm, the thin solidline shows the actual steering angle (the handle angle in the presentembodiment) Or, and the broken line shows the steering torque Tt.

As well,

in FIG. 22, the assist control output gradual-change gain Gft1 is 0%,that is, the assist control does not operate. Further, FIG. 22 shows anexample of a simulation for describing a situation where the actualsteering angle θr and the steering torque Tt are changed as the driver'starget angle θarm is changed.

With respect to changes of the actual steering angle θr and the steeringtorque Tt in the case of inputting the driver's target angle θarm inthis way, the case of performing the velocity control with thePI-control without the steering intervention compensation and the caseof performing the steering intervention compensation are compared. Inthe former case, the assist control output gradual-change gain Gft1 andthe assist map gradual-change gain Gft2 are set to 100% in comparisonwith the present embodiment, and the difference between the integralmethods is verified. In the latter case, the assist control outputgradual-change gain Gft1 is set to 0%. Further, in a conventional priorart (for example, Patent Document 1), an assist control command value is0 [deg] in the steering control before the switching, however, since thesteering intervention in this case is presumed to be more difficult thanin the former case, this case is omitted.

A result of the simulation is shown in FIG. 23. The vertical axisindicates a steering torque [Nm], the horizontal axis indicates anactual steering angle [deg], the broken line shows the case without thesteering intervention compensation, and the solid line shows the casewith the steering intervention compensation. In the steeringintervention compensating section 350, the steering interventioncompensating map is set so as to linearly change from an origin.

As shown by the broken line in FIG. 23, in the case without the steeringintervention compensation, the steering can be performed until theactual steering angle θr becomes 7.5 [deg], however, since the velocitydeviation (the deviation between the steering angular velocity commandvalue and the actual steering angular velocity) is continuously storedby the influence of the integral of the PI-control in the velocitycontrol, the steering forcibly returns to the position corresponding tothe steering angle command value θref (=0 [deg]) eventually. Moreover, avery large steering torque being larger than or equal to 15 [Nm] occurs,and the steering by the driver becomes difficult.

On the contrary, as shown by the solid line in FIG. 23, in the case withthe steering intervention compensation, the steering can be performeduntil the actual steering angle θr becomes about 22 [deg], and does notreturn to the position corresponding to the steering angle command valueθref (=0 [deg]). This is because the steering angular velocity commandvalue ωref2 outputted from the steering intervention compensatingsection 350 is added to the steering angular velocity command valueωref1 outputted from the position control section 340, and the velocitydeviation between the steering angular velocity command value ωref andthe actual steering angular velocity ωr in the steering state balancesin the vicinity of “0”. Thus, the function of the steering interventioncompensating section 350 enables the steering intervention by thedriver. Further, an increase in the steering intervention compensationgain Ktp enables easier steering.

Next, an effect for a handle vibration occurring in the steering anglecontrol performed during the automatic steering in the case ofperforming only the steering angle control without the steeringintervention by the driver (the handle manual input torque “Th=0 [Nm]”),will be described.

Before describing the effect for the handle vibration, followability tothe steering angle command value θref and the effects due to thereference model and the FF filter in the position control section 340will be described in order to describe a situation where the actualsteering angle θr follows the steering angle command value θref. Even inthe simulation for verifying the present effects, in order to verifyonly the steering angle control characteristic, the setting that neitherthe steering intervention by the driver nor the steering interventioncompensation is performed is adopted. FIG. 24 shows an example of a timeresponse in the case of changing the steering angle command value θreffrom 0 [deg] to 100 [deg] in a ramp state. In FIG. 24, the vertical axisindicates a steering angle [deg], the horizontal axis indicates a time[sec], and the dotted line shows the steering angle command value θref.Situations of responses of the target steering angle θt outputted fromthe handle vibration eliminating section 330 having a primary LPF whosecutoff frequency is 2 [Hz] and the actual steering angle θr to thesteering angle command value θref, are shown by the thin solid line andthe thick solid line respectively. From FIG. 24, it is found out thatthe target steering angle θt and the actual steering angle θr follow thesteering angle command value θref.

From the above description, it can be said that both the steeringintervention and the follow-up of the steering angle during theautomatic steering can be achieved.

The simulation of the reference model and the FF filter of the positioncontrol section 340, first, specifies the frequency characteristic ofthe transfer function P_(ωθ) from the steering angular velocity commandvalue ωref to the actual steering angle θr by a frequency sweep or theidentification by fitting with a transfer function. The result is shownin FIGS. 25A and 25B. FIG. 25A shows a gain characteristic of thetransfer function P_(ωθ), FIG. 25B shows a phase characteristic of thetransfer function P_(ωθ), the thin solid line shows the result of thefrequency sweep, and the thick solid line shows the result of thefitting. Moreover, the transfer function P_(ωθ) of the result of thefitting is the below Expression 3.

$\begin{matrix}{P_{\omega\theta} = {\frac{\theta\; r}{\omega_{ref}} = \frac{7316.2}{{0.053516\mspace{11mu} s^{4}} + {3.4464\mspace{11mu} s^{3}} + {437.25\mspace{11mu} s^{2}} + {7316.2\mspace{11mu} s}}}} & \left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In the transfer function G_(model) of the reference model section 341defined by the Expression 1, the cutoff frequencies f_(m1) and f_(m2)are set to 10 [Hz] and 20 [Hz] respectively. The transfer function Gf ofthe FF filter is calculated based on the Expression 2. Frequencycharacteristics of the transfer function G_(model), the transferfunction P_(ωθ) and the transfer function Gf of the FF filter are shownin FIGS. 26A and 26B under such settings. FIG. 26A shows gaincharacteristics, and FIG. 26B shows phase characteristics.

Since the followability of the steering angle control (the followabilityof the actual steering angle θr to the steering angle command valueθref) can be cited as an effect by the reference model and the FFfilter, a simulation of changing the steering angle command value θreffrom 0 [deg] to 100 [deg] in a ramp state at the vehicle speed V equalto 60 [km/h] under the above settings, is performed. The result is shownin FIG. 27. In FIG. 27, the vertical axis indicates a steering angle[deg], the horizontal axis indicates a time [sec], and the broken lineshows the steering angle command value θref. With respect to thissteering angle command value θref, a time response of an actual steeringangle calculated based on a value obtained by simply multiplying thesteering angle deviation (the deviation between the target steeringangle θt and the actual steering angle θr) with a gain, is shown by thethin solid line, a time response of an actual steering angle calculatedby the model reference control performed by the reference model and theFF filter in the position control section 340, is shown by the thicksolid line, and a time response of the target steering angle θt1outputted from the reference model section 341 is shown by a dottedline.

From FIG. 27, it is found out that the followability is improved by theset reference model and FF filter, and the actual steering angle of themodel reference control corresponds well with the target steering angleθt1 being an output of the reference model, compared with the resultobtained by simply multiplying the gain, which is shown by the thinsolid line. Although the effect due to the reference model and the FFfilter is shown in FIG. 27, it can be verified that the actual steeringangle θr sufficiently follows the steering angle command value θref evenin the case of simply multiplying the steering angle deviation with thegain (shown by the thin solid line).

In the simulation for verifying the effect for the handle vibration, adifference of a time response of the torsion bar torque between with andwithout the handle vibration eliminating section 330 and the handledamping section 380, is examined in the case of performing the steeringangle control with respect to the same steering angle command value θrefas shown in FIG. 27. The handle vibration eliminating section 330 usesthe primary LPF whose cutoff frequency is 2 [Hz]. The handle dampingsection 380 uses the gain Kv by which a torque converted into a columnshaft becomes equivalent to 10 [Nm] for the torsion bar torque being 1[Nm], and performs phase lead compensation by a primary filter where acutoff frequency of a numerator is 10 [Hz] and a cutoff frequency of adenominator is 20 [Hz]. The result is shown in FIG. 28. In FIG. 28, thevertical axis indicates the torsion bar torque [Nm], the horizontal axisindicates the time [sec], the solid line shows the case with thevibration countermeasure by the handle vibration eliminating section 330and the handle damping section 380, and the dotted line shows the casewithout the vibration countermeasure. From FIG. 28, it is found out thatthe handle vibration is suppressed by the handle vibration eliminatingsection 330 and the handle damping section 380.

As the last of the description of the effect, an effect for a problemthat the integral value of the I-control accumulates excessively due toan increase in the steering angular velocity at the start of thesteering angle control and the steering angle control command value maybecome excessive (a problem in Patent Document 3 and so on), will bedescribed.

FIG. 29 shows time changes of the target steering angular velocity ωt,the gradual-change gains and the limit value used at the velocitycommand value variable-limiting section 360 when the state changes fromthe manual steering state to the automatic steering state. Assuming thatthe velocity control gradual-change gain Gfa2 and the velocity commandgradual-change gain Gfa3 are changed in synchronization with thesteering angle control output gradual-change gain Gfa1, only thegradual-change gain Gfa1 is shown in FIG. 29. Assuming that the assistcontrol output gradual-change gain Gft1 and the assist mapgradual-change gain Gft2 are also changed in synchronization with thegradual-change gain Gfa1, only the situation of the change of thegradual-change gain Gft1 is shown as a reference. Further, the magnitudeof the limit value used at the velocity command value variable-limitingsection 360 is set so as to be fixed at a small value when thegradual-change gain Gfa3 is smaller than the predetermined threshold,and gradually increase when the gradual-change gain Gfa3 is larger thanor equal to the predetermined threshold.

The steering angular velocity command value ωref is multiplied with thevelocity command gradual-change gain Gfa3, is limited at the velocitycommand value variable-limiting section 360, and becomes the targetsteering angular velocity ωt. When the shift from the manual steeringstate to the automatic steering state is started, the gradual-changegain Gfa3 gradually increases from “0”, and the target steering angularvelocity ωt also gradually increases from “0”. After that, when thesteering angular velocity command value ωrefg inputted into the velocitycommand value variable limiting section 360 reaches the limit value (thelimit value “a”) at the time point t10, the target steering angularvelocity cot becomes constant at the limit value “a”, however, thegradual-change gain Gfa3 continuously increases. When the gradual-changegain Gfa3 becomes the predetermined threshold at the time point t11, thelimit value gradually increases, and the target steering angularvelocity cot also increases correspondingly. When the gradual-changegain Gfa3 becomes 100% at the time point t12, in addition, the limitvalue becomes the limit value “b” at the time point t13, the targetsteering angular velocity cot changes within the limit value “b”. Sincethe target steering angular velocity cot is limited by the limit value“a” and is limited by multiplication of the velocity controlgradual-change gain Gfa2 at the steering angular velocity controlsection 370 between the time points t10 and t13, excessive accumulationof the integral value in the steering angular velocity control section370 is suppressed, and the current command value causing theuncomfortable feeling to the driver as an output of the steering anglecontrol can be reduced. After the transition of the limit value is ended(that is, after the time point t13), the steering angular velocitycommand value ωref is not limited by the gradual-change gain Gfa3 andthe velocity command value variable limiting section 360, and a signalin the steering angular velocity control section 370 is not also limitedby the gradual-change gain Gfa2, so that it is possible to shift to thenormal steering angle control.

As well, with respect to the multiplications of the respectivegradual-change gains (Gfa1 to Gfa4, Gft1 and Gft2) in the firstembodiment, in such a case of focusing on a cost more than the effect bythe multiplication of the gradual-change gain, it is possible to leaveat least one multiplication and omit other multiplications. Further, therespective limiting sections (the steering angle command valuevariable-limiting section, the variable-rate limiting section, thevelocity command value variable-limiting section and the steering anglecontrol current command value-limiting section) are also possible toomit in the same case or the like. When the steering angle command valuevariable-limiting section 310, the variable-rate limiting section 320and the multiplying section 391, in addition, the handle vibrationeliminating section 330 are omitted, the steering angle command valueθref is inputted into the position control section 340 as the targetsteering angle θt. When the multiplying section 392 and the velocitycommand value variable-limiting section 360 are omitted, the steeringangular velocity command value ωref is inputted into the steeringangular velocity control section 370 as the target steering angularvelocity ωt.

The second embodiment of the present invention will be described.

In the second embodiment, a dead band to the steering torque is set inthe steering intervention compensating section in order to expedite themanual input judgment. To achieve this, compared with the firstembodiment, a configuration of the steering intervention compensatingsection is different. A configuration example of the steeringintervention compensating section 550 in the second embodiment is shownin FIG. 30. Compared with the steering intervention compensating section350 in the first embodiment shown in FIG. 11, a dead band settingsection 553 is inserted between the steering intervention phasecompensating section 351 and the compensating map section 352. Thesteering torque Tt1 outputted from the steering intervention phasecompensating section 351 is inputted into not the compensating mapsection 352 but the dead band setting section 553, and a steering torqueTt2 outputted from the dead band setting section 553 is inputted intothe compensating map section 352. Other configurations are the same asthose of the first embodiment.

The dead band setting section 553 sets the dead band to the steeringtorque Tt1 and outputs the operated steering torque as the steeringtorque Tt2. For example, the dead band shown in FIG. 31 is set. That is,in the case of not setting the dead band, the steering torque Tt1 isoutputted as the steering torque Tt2, as shown by the broken line. Bysetting the dead band in the range that the steering torque Tt1 is inthe vicinity of zero, as shown by the solid line, the value of thesteering torque Tt2 is zero in the above range and changes the valuewith the same gradient of the broken line out of the above range so thatthe steering torque Tt2 changes in conjunction with the steering torqueTt1. By setting such a dead band, the steering angular velocity commandvalue ωref2 outputted from the compensating map section 352 at the rearstage is also zero in the above range and the steering interventioncompensation is not performed. That is, when the steering interventionby the driver is occurred, the steering torque easily increases up tothe threshold of the dead band. As a result, the manual input judgementis performed at an early timing. The magnitude of the positive thresholdin the dead band may not the same as that of the negative threshold inthe dead band.

Compared with the operating example of the first embodiment, anoperating example of the second embodiment is different in that theoperation of the dead band setting section 553 is added to theoperations of the steering intervention compensating section duringoperating the steering angle control section. That is, in the operatingexample of the steering angle control section 300 in the firstembodiment shown in FIGS. 19 and 20, the second embodiment performs thesame operations as the first embodiment until the Step S610 where thesteering intervention phase compensating section 351 converts thesteering torque Tt into the steering torque Tt1, and the steering torqueTt1 is inputted into the dead band setting section 553. The dead bandsetting section 553 sets the dead band to the steering torque Tt1 byusing the characteristic shown in FIG. 31 and outputs the operatedsteering torque as the steering torque Tt2 to the compensating mapsection 352. The operations (from Step S620) after the vehicle speed Vand the steering torque Tt2 are inputted into the compensating mapsection 352 are the same as the first embodiment.

The dead band setting section 553 may be disposed at the front stage ofthe steering intervention phase compensating section 351. Even if thedead band setting section 553 is removed and the map having the deadband is used as the steering intervention compensating map (the map thatthe output value within the setting range is zero to the input torque),the same effect can be obtained.

An effect of the dead band in the steering intervention compensation byadding the dead band setting section 553 in the second embodiment willbe described.

Assuming that the steering for the emergency avoidance is performed, thesimulation is performed by inputting the driver's target angle θarm asshown in FIG. 32. In FIG. 32 as well as FIG. 22, the vertical axisindicates the angle [deg] and the steering torque [Nm], the horizontalaxis indicates the time [sec], the thick solid line shows the driver'starget angle θarm, and the thin solid line and the broken line show thetime responses of the actual steering angle θr and the steering torqueTt to the time change of the driver's target angle θarm, respectively.As shown in the thick solid line of FIG. 32, the driver's target angleθarm rises from 0.5 [sec] and changes up to 60 [deg].

In the case that such a driver's target angle θarm is inputted, the casethat positive and negative thresholds having “+2.5 [Nm]” and “−2.5 [Nm]”of the steering torque Tt1 are set as the dead band is compared with thecase of no dead band. The compared result is shown in FIG. 33. Themanual input judging section 223 in the switch-judgment andgradual-change gain generating section 220 smooths the steering torqueTt by using the smoothing filter section 225 where the primary LPF whosecutoff frequency is 1.5 [Hz] and the primary LPF whose cutoff frequencyis 3.0 [Hz] are connected in series. When the absolute value |Tt′| ofthe smoothed steering torque Tt′ is larger than or equal to thethreshold Tth that is set to 2 [Nm], it is judged that “presence of themanual input”.

In FIG. 33, the vertical axis indicates the steering torque [Nm], thehorizontal axis indicates the time [sec], the thick solid line shows thesteering torque Tt in the case without the dead band, the broken lineshows the steering torque Tt in the case with the dead band, the dottedline shows the steering torque Tt′ in the case with the dead line, andthe thin solid line shows the steering torque Tt′ in the case withoutthe dead line. In FIG. 33, the portions that are enclosed in the circlesare the time when the absolute value of the steering torque Tt′ reachesthe threshold Tth. The timings when “presence of the manual input” isjudged are about 0.7 [sec] in the case with the dead band and about 0.8[sec] in the case without the dead band. The case with the dead band canbe verified by about 0.1 [sec] faster than the case without the deadband. Accordingly, by disposing the dead band, faster judgement can beperformed.

Other embodiments of the present invention will be described.

Although the multiplication of the velocity control gradual-change gainGfa2 at the steering angular velocity control section 370 is performedto the control amount Ir1 outputted from the integrating section 373 inthe first embodiment, it can be performed to the steering angle controlcurrent command value IrefW outputted from the subtracting section 375.

FIG. 34 shows a configuration example (the third embodiment) of thesteering angular velocity control section in the case of multiplying thesteering angle control current command value IrefW with the velocitycontrol gradual-change gain Gfa2. Compared with the steering angularvelocity control section 370 in the first embodiment shown in FIG. 14,in a steering angular velocity control section 670 of the thirdembodiment, the multiplying section 376 is provided not behind theintegrating section 373 but behind the subtracting section 375, and theother configurations are the same.

An operating example of the steering angular velocity control section670 in the third embodiment performs the same operations as theoperating example of the first embodiment shown in FIGS. 19 and 20 untilthe Step S710 where the integrating section 373 integrates the operationamount D1 and calculates the control amount Ir1, after that, the controlamount Ir1 is inputted into the subtracting section 375, and a controlamount Ir3′ is calculated as a deviation (=Ir1−Ir2) between the controlamounts Ir1 and Ir2. The multiplying section 376 multiplies the controlamount Ir3′ with the velocity control gradual-change gain Gfa2, andoutputs the multiplied result as the steering angle control currentcommand value IrefW to the adding section 394. The operations (from theStep 750) after that are the same as the first embodiment.

It is possible to perform the multiplication of the velocity controlgradual-change gain Gfa2 at another position in the steering angularvelocity control section 370.

A configuration example (the fourth embodiment) of a steering angularvelocity control section shown in FIG. 35 multiplies the deviation ωeoutputted from the subtracting section 374 with the velocity controlgradual-change gain Gfa2. Compared with the steering angular velocitycontrol section 370 in the first embodiment shown in FIG. 14, in asteering angular velocity control section 770 of the fourth embodiment,the multiplying section 376 is provided not behind the integratingsection 373 but behind the subtracting section 374, and the otherconfigurations are the same.

An operating example of the steering angular velocity control section770 in the fourth embodiment performs the same operations as theoperating example of the first embodiment shown in FIGS. 19 and 20 untilthe Step S690 where the subtracting section 374 calculates the deviationωe between the target steering angular velocity cot and the actualsteering angular velocity ωr, and the deviation ωe is inputted into notthe gain multiplying section 371 but the multiplying section 376. Themultiplying section 376 multiplies the deviation ωe with the velocitycontrol gradual-change gain Gfa2, and outputs the multied result as adeviation ωe1 to the gain multiplying section 371. The operations afterthat are the same as the first embodiment except to remove the StepS720.

In the above embodiments (the first to the fourth embodiments), thevelocity command value variable-limiting section 360 sets the limitvalues depending on the velocity command gradual-change gain Gfa3, andswitches the limit values when the Gfa3 becomes the predeterminedthreshold. However, a velocity command value variable limiting sectionuses the steering angle control output gradual-change gain Gfa1 insteadof the gradual-change gain Gfa3, and may switch the limit values whenthe gradual-change gain Gfa1 becomes 100%. In a configuration (the fifthembodiment) of this case, the gradual-change gain Gfa1 is inputted intothe velocity command value variable-limiting section instead of thegradual-change gain Gfa3, and the other configurations are the same asthe other embodiments. In an operation of the fifth embodiment, ajudgment operation of determining limit values at the velocity commandvalue variable limiting section (the Step S650 shown in FIG. 20) ischanged to a confirmation of whether or not the gradual-change gain Gfa1is smaller than 100%. In the fifth embodiment, time changes of thetarget steering angular velocity ωt, the gradual-change gains and thelimit value of the velocity command value variable-limiting section inthe case of changing the state from the manual steering state to theautomatic steering state, become as shown in FIG. 36. Compared with thetime changes shown in FIG. 29, the limit value of the velocity commandvalue variable-limiting section gradually increases from the time pointt12 where the gradual-change gain Gfa1 becomes 100%, and the targetsteering angular velocity cot also increases correspondingly.

The invention claimed is:
 1. An electric power steering apparatus that drives a motor based on a current command value, and performs an assist control and a steering angle control for a steering system by drive-controlling said motor, comprising: a steering angle control section that calculates a steering angle control current command value for said steering angle control based on at least a steering angle command value and an actual steering angle, wherein said steering angle control section comprises: a position control section to calculate a basic steering angular velocity command value based on said steering angle command value and said actual steering angle; a steering intervention compensating section to obtain a compensatory steering angular velocity command value for a steering intervention compensation depending on a steering torque; and a steering angular velocity control section to calculate said steering angle control current command value based on a steering angular velocity command value calculated from said basic steering angular velocity command value and said compensatory steering angular velocity command value, and an actual steering angular velocity, wherein said position control section comprises: a reference model section to convert said steering angle command value into a target steering angle using a reference model; a proportional gain section to calculate a first basic steering angular velocity command value by multiplying a deviation between said target steering angle and said actual steering angle with a proportional gain; and a filter section to convert said steering angle command value into a second basic steering angular velocity command value by using a feedforward filter (an FF filter), wherein said basic steering angular velocity command value is calculated by adding said second basic steering angular velocity command value to said first basic steering angular velocity command value, wherein said steering intervention compensating section comprises a compensating map section having a steering intervention compensating map that determines a characteristic of said compensatory steering angular velocity command value to said steering torque, and said steering intervention compensating section obtains said compensatory steering angular velocity command value by said steering torque through said compensating map section, and wherein said electric power steering apparatus calculates said current command value using at least said steering angle control current command value.
 2. The electric power steering apparatus according to claim 1, wherein said steering intervention compensating section further includes a dead band setting section that sets values to said steering torque within a predetermined range to zero, and said compensatory steering angular velocity command value is obtained from said steering torque through said dead band setting section and said compensating map section.
 3. The electric power steering apparatus according to claim 1, wherein said steering intervention compensating map has a characteristic that said compensatory steering angular velocity command value decreases as a vehicle speed increases.
 4. The electric power steering apparatus according to claim 2, wherein said steering intervention compensating map has a characteristic that said compensatory steering angular velocity command value decreases as a vehicle speed increases.
 5. The electric power steering apparatus according to claim 1, wherein said steering intervention compensating section further comprises a steering intervention phase compensating section that performs a phase compensation to said steering torque, and said steering intervention compensating section obtains said compensatory steering angular velocity command value with said steering torque through said steering intervention phase compensating section.
 6. The electric power steering apparatus according to claim 1, wherein said steering angular velocity control section calculates said steering angle control current command value with an integral proportional control (an I-P control) by using said steering angular velocity command value and said actual steering angular velocity.
 7. The electric power steering apparatus according to claim 1, wherein a filter gain of said FF filter changes depending on a vehicle speed.
 8. The electric power steering apparatus according to claim 1, further including an assist control section to calculate an assist control current command value for said assist control based on at least said steering torque, wherein said current command value is calculated from said assist control current command value and said steering angle control current command value.
 9. The electric power steering apparatus according to claim 8, wherein for adjusting said assist control current command value, said assist control current command value is multiplied with an assist control output gradual-change gain.
 10. The electric power steering apparatus according to claim 8, wherein an assist map output current obtained in said assist control section is multiplied with an assist map gradual-change gain.
 11. The electric power steering apparatus according to claim 9, wherein an assist map output current obtained in said assist control section is multiplied with an assist map gradual-change gain.
 12. The electric power steering apparatus according to claim 9, wherein only said steering angle control is performed to said steering system by multiplying said assist control current command value with said assist control output gradual-change gain whose value is zero.
 13. The electric power steering apparatus according to claim 1, wherein said steering angle control section further includes a steering angle control current command value limiting section to limit said steering angle control current command value with a preset limit value.
 14. The electric power steering apparatus according to claim 2, wherein said steering angle control section further includes a steering angle control current command value limiting section to limit said steering angle control current command value with a preset limit value.
 15. The electric power steering apparatus according to claim 3, wherein said steering angle control section further includes a steering angle control current command value limiting section to limit said steering angle control current command value with a preset limit value. 